1. Field of the Invention
The present invention is directed to a process for sealing and/or priming concrete with an aqueous polyisocyanate and to the concrete obtained in accordance with this process.
2. Description of the Prior Art
It is known to use moisture-curing NCO prepolymers such as those disclosed in U.S. Pat. No. 3,792,023 to protect concrete from the degrading effects of water, salt and acid rain. However, in order to penetrate concrete, the prepolymer is usually diluted to a solids content of 10 to 30% by weight with organic solvents which are inert to isocyanate groups. The solvents not only represent a flammability hazard, but also create an environmental problem.
Another restriction on using the NCO prepolymers is that the concrete has to be absolutely dry. If water is present, the hydrophobic polyisocyanate solutions cannot penetrate the concrete and foaming occurs on the concrete surface. Therefore, the NCO prepolymers are not suitable for use as sealants on wet or "green" concrete.
Sealants are applied to concrete before it is fully cured ("green" concrete) in order to prevent the rapid evaporation of water from the concrete and, thus, improve the cure and ultimately the final strength of the concrete. Presently, fluorinated hydrocarbons or oils are used to seal "green" concrete. While these sealants are effective in preventing the evaporation of water, they do not protect the concrete from water, salt and acid rain. In order to achieve such protection, a top coat is necessary. However, commercial top coats do not adhere to fluorinated hydrocarbon or oil-based sealants which means that the sealant must be removed, e.g., by sand blasting, before application of a protective top coat.
Accordingly, an object of the present invention is to provide a composition which functions as a sealant to prevent the evaporation of water and improve the cure and strength of green concrete. A further object of the present invention is to provide a sealant which also functions as a primer such that a firmly adhering top coat can be directly applied to the sealant.
These objects can be achieved in accordance with the present invention by using certain aqueous polyisocyanate dispersions as the primer/sealant. Surprisingly, the polyisocyanate dispersions can penetrate and seal wet concrete prior to the polyisocyanate reacting with the dispersion water or the water present in the wet concrete.
U.S. Pat. No. 4,904,522 discloses the use of such polyisocyanate dispersions as binders for fiberglass. However, there is no suggestion in this patent to use the polyisocyanate dispersions for the treatment of concrete nor would it be possible to determine from this reference that the polyisocyanate dispersions could function as primers and sealants for concrete.
Copending application. U.S. Ser. No. 07/529,056, filed May 25, 1990, is directed to reducing the isocyanate content of aqueous polyisocyanate dispersions by reacting the dispersed polyisocyanates reacted with monoamines containing at least one hydroxyl group in order to improve their effectiveness as binders for fiberglass. Copending application is directed to increasing the pot life of aqueous polyisocyanate dispersions by reacting the dispersed polyisocyanates with polyamines in order to encapsulate the dispersed polyisocyanates and reduce their reactivity to water. Copending application is directed to to an improved method for reducing the isocyanate content of aqueous polyisocyanate dispersions by reacting the dispersed polyisocyanates with both monoamines containing at least one hydroxyl group and polyamines. None of the these copending applications suggest the use of the polyisocyanate dispersions for the treatment of concrete not do they provide any indication that the polyisocyanate dispersions could function as primers and sealants for concrete.